The invention concerns methods and an arrangement related to a radio communication system. More specifically, the invention relates to a method of transmitting radio signals in a terrestrial cellular radio communication network using power amplification resources of a base station in a highly flexible and efficient way. The invention includes a terrestrial radio communication network comprising the necessary means to implement the method. The invention also includes a method of dimensioning the power amplification resources of the base station.
A substantial part of the cost of a base station in a terrestrial radio communication system is related to the power amplification of radio signals transmitted by the base station.
Traditionally base stations have been equipped with so called single carrier power amplifiers (SCPA), each SCPA amplifying a single radio frequency carrier and designed so that it can deliver enough power to support communication with a mobile station positioned at the cell border.
An alternative way of designing the power amplification part of a base station, which is becoming increasingly common, is to equip the base station with so called multi carrier power amplifiers (MCPA) each capable of amplifying a radio signal comprising multiple radio frequency carriers. Typically a base station serving a single cell is equipped with one MCPA or one group of MCPAs working in parallell, while a base station serving a plurality of (sector) cells is equipped with one MCPA or one group of MCPAs working in parallell for each cell.
There are several advantages of using MCPAs instead of SCPAs in a base station. One advantage afforded by using MCPAs is that it is possible to benefit from functions such as Down link Power Control (DPC) and discontinuous transmission (DTX) which give statistical reductions in the total output power required to support a certain number of radio frequency carriers. Use of the DPC-function is estimated to give a statistical reduction in the required output power of about 4-6 dB while use of the DTX-function is estimated to cause a reduction of about 3-4 dB, in total a reduction of upto about 10 times. This means that an MCPA designed to support a certain number of carriers can be designed to deliver significantly less output power than the total output power required if a plurality of SCPAs were to support the same number of carriers.
In order to achieve the full statistical reduction afforded by the DPC- and DTX-functions, it is however necessary that the number of radio frequency carriers in the cell is high.
U.S. Pat. No. 5,854,611 discloses a base station, e.g. an Advanced Mobile Phone Service (AMPS) base station, serving a single cell in which a plurality of narrow antenna beams, e.g. 10 beams, are used to provide radio coverage in the cell. The base station comprises a first power sharing network coupled to a plurality of linear power amplifiers, which in turn are coupled to a second power sharing network. The first power sharing network equally distributes a received input signal from one of its input ports to the plurality of linear power amplifiers coupled thereto in substantially equal power levels and being staggered in phase relative to one another. The linear amplifiers independently amplify each respective output signal from the first power network. The second power sharing network receives the phase staggered amplified signals and provides an output signal having an average power level relative to the combined power level of the phase staggered amplified input signals to the second power sharing network. The output signal from the second power sharing network is then radiated in one of the narrow antenna beams. The base station and antenna system disclosed in U.S. Pat. No. 5,854,611, provides the advantages associated with the use of narrow antenna beams while avoiding the need for poorly utilized dedicated power amplifiers for each individual narrow antenna beam.
U.S. Pat. No. 4,618,813 describes a power amplifying apparatus in which signals to a plurality of input terminals, which are to be individually provided to a plurality of output terminals, share the sum of the output power capacities of a plurality of amplifiers. The patent specification briefly discusses an application of the power amplifying apparatus in a multi-beam satellite communication system
The problem dealt with by the present invention is how to provide a cost efficient and flexible way of performing radio signal power amplification in a base station in a terrestrial radio communication network.
The problem is solved essentially by a method and arrangement in which a common set of multi carrier power amplifiers are used to amplify radio signals transmitted by a base station in different cells.
More specifically, the problem is solved in the following manner. A first set of low power radio signals comprising at least a first and a second radio signal is generated. The first radio signal is generated so as to consist of radio carrier components having frequencies allocated for use in a first cell of the cellular radio communication network. The second radio signal is generated so as to consist of radio carrier components having frequencies allocated for use in a second cell of the cellular radio communication network. A second set of amplified radio signals corresponding to the first set of radio signals is generated by amplifying the first set of radio signals using the common set of multi carrier power amplifiers. The second set of amplified radio signals is radiated in associated antenna beams, wherein the amplified radio signal corresponding to the first radio signal is radiated in an antenna beam associated with the first cell and the amplified radio signal corresponding to the second radio signal is radiated in an antenna beam associated with the second cell.
A general object of the invention is to provide a cost efficient and flexible way of performing radio signal power amplification in a base station in a terrestrial radio communication network.
Another object is to reduce the maximum total output power a base station needs to deliver in order to service a certain number of radio carriers or to serve more radio carriers given a certain maximum total output power.
Still another object is to enable reallocation of output power between different cells served by a base station.
Yet another object is to enable adaptation of both the available output power and number of radio carrier frequencies in a cell as demand for capacity changes in the cell.
A general advantage afforded by the invention is that it provides a cost efficient and flexible way of performing radio signal power amplification in a base station in a terrestrial radio communication network.
A more specific advantage offered by the invention is that the total maximum output power of a base station servicing a certain number of radio carriers can be reduced. This implies that equipment cost, power consumption, size and weight of the base station can be reduced.
Still another advantage provided by the invention is that output power can be reallocated between different cells served by a base station.
Yet another advantage of the invention is that both the available output power and number of radio carrier frequencies in a cell can be adapted as demand for capacity changes in the cell.
The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings.